This invention is generally concerned with a process for in-reactor stabilization of olefins resulting in polyolefins which do not need extrusion pelletization. The present invention is directed toward an improved method for stabilizing polyolefins, in particular, stabilizing polypropylene by a method wherein during polymerization in the reactor, a procatalyst component, an alkyl aluminum-antioxidant compound and an acid acceptor is added to the olefin monomer(s), and then polymerized in association with a cocatalyst, selectivity control agent and optionally, another electron donor. The resultant polymer can be directly sold to customers without further extrusion. It is anticipated that this novel process can be used for preparing powder or alternatively granules of polypropylene (containing stabilizer) having diameters of 1-5 mm.